The men, described as "beyond human instinct" by a judge, preyed on the families of youngsters to gain access to them, in one case grooming a mother and father before their baby's birth.

Chat logs revealed the gang would offer advice on using "date rape" drugs or over-the-counter medication to drowse children and babies.

Hollyson, from Bedfordshire, was one of seven men convicted of 29 child sex abuse offences, including the multiple rape of an 11-month-old.

A spokeswoman for the Prison Service said: "HMP Bristol prisoner James King (04/07/84) was found unresponsive in his cell on Friday 15 January.

"Prison staff attempted CPR and paramedics attended, but he died in hospital on Sunday 17 January.

"As with all deaths in custody, the independent Prisons and Probation Ombudsman will conduct an investigation."

It is understood that Hollyson, previously known as Robin Fallick, changed his name to James King and that his death is not being treated as suspicious.

The other men convicted were John Denham, 50, from Wiltshire, Matthew Stansfield, 35, from Hampshire, Adam Toms, 33, from Somerset, Christopher Knight, 35, from Manchester, David Harsley, 51, from Yorkshire, and Matthew Lisk, 33, from Sussex.

Judge Julian Lambert jailed the men, including two who are HIV positive, for terms ranging from two to 24 years at Bristol Crown Court in September.

Hollyson received the 24-year sentence after pleading guilty to three counts of raping a child under the age of 13.

He also admitted three counts of conspiracy to rape a child under 13, sexual assault of a child under 13, and taking, showing, possessing indecent images of children and extreme pornography.

The court heard how Hollyson befriended a couple with a baby and was allowed to babysit in 2013.

He boasted of repeatedly raping the boy from the age of three months - filming himself doing so between December 2013 and January 2014.

In May 2014, Hollyson, Stansfield and Toms took turns to rape and sexually assault the baby, while sharing footage online.

Judge Lambert told him: " You determined cruelly and callously to exploit a family and prey on their baby for your perverted sexual purposes. You were keen to involve others in your deviant sexual activity. You determined to share the abuse of the baby with other perverted men and to publish your corrupt sexual exploits in the darkest parts of cyberspace."